Explosion-proof lead-in structure



Jan. 30, 1968 THOMPSON 3,366,271

EXPLOS IONPROOF LEAD- IN STRUCTURE Filed Jun 7, 1965 FlG-3- 6 FIG-4.-F|G.5.

26 3| ATTORNEYS.

f INVENTOR. O ,43% ARDEN 'TZTHOMPSON.

United States Patent 3,366,271 EXPLOSION-PROOF LEAD-IN STRUCTURE Arden'1. Thompson, Elmhurst, IlL, assignor to Lab-Line Instruments, Inc.,Melrose Park, 11]., a corporation of Delaware Filed June 7, 1965, Ser.No. 462,029 7 Claims. (Cl. 2213-88) This invention relates toexplosion-proof lead-in structure, and more particularly to a wallhaving a pass-age for a lead-in element, the wall and passage such thatflame and hot gases resulting from an explosion on one side of the wallwill not be communicated to the other side.

The wall of the invention advantageously may be used, for example, asone wall of a housing enclosing the thermostatic control switch for thecompressor motor of an electric refrigerator. Such a housing, whethermounted inside or outside of the refrigerator, is subject toinfiltration by explosive gases present in the surrounding atmosphere.Electric arcing or sparking incident to switch operation tends to causeexplosion of any such gases within the housing, and it therefore isessential to prevent the escape of flame or hot gases to the outsideatmosphere, which, in the circumstances, also might be of explosivecharacter.

A thermostatic control switch requires a lead-in element, such as acapillary tube, that extends between the switch and a remote regionexperiencing the temperature conditions to be sensed. In the case of anelectric refrigerator, a capillary tube extends from a sensing regionwithin the refrigerator to the thermostatic switch within the housing,and this tube must extend through the switch housing or box in asufficiently sealed manner so that an explosion within the housing willnot be communicated to the exterior.

The sealing problem solved by this invention is one that heretofore hasbeen solved by complex arrangements requiring specialized apparatus andconsiderable in the way of labor for installation. In general, thesearrangements have proved unsatisfactory for various reasons, one ofwhich is inordinate expense.

One object of the invention, therefore, is to provide explosion-prooflead-in structure that is highly effective and reliable in use.

Another object is to provide explosion-proof lead-in structure that maybe constructed and installed easily and quickly at great savings in costover arrangements previously used.

Other objects, advantages and details of the invention will be apparentas the description proceeds, reference being bad to the accompanyingdrawing wherein one form of the invention is shown. It will beunderstood that the description and drawing are illustrative only, andthat the scope of the invention is to be measured by the appendedclaims.

In the drawing:

FIG. 1 is a perspective view of a housing having a wall employing theexplosion-proof lead-in structure of the invention.

FIG. 2 is a side elevational view of the housing shown in FIG. 1 with aportion of the explosion-proof lead-in structure shown in phantom forclarity.

FIG. 3 is a fragmentary front elevational view of the housing.

FIG. 4 is a front elevational view of a seal plate forming part of theinvention.

FIG. 5 is a rear elevational view of the seal plate shown in FIG. 4.

Referring to the drawing, the explosion-proof lead-in structure of theinvention is shown embodied in a housing 6 enclosing, for example, thethermostatic control switch (not shown) for an electric refrigerator, aportion of :an adjacent wall of which is shown at 7. Housing 6 may haveone or more laterally extending lugs 8 for mounting the housing on wall7.

Access to the interior of the illustrated housing 6 for installing andinspecting an inclosed switch is provided by means of a closure disk 9suitably threaded in an opening in housing wall 10.

The explosion-proof lead-in structure of the invention is incorporatedin one of the housing walls, for example, wall 15. As best shown in FIG.2, wall 15 has an opening 16 for passing a lead-in element, as will beseen. Opening 16 is located more or less centrally of wall 15, but inany event it is spaced a substantial distance from all edges of thewall.

Housing 6 is of such structural strength as to withstand the pressuresthat may be generated as the result of an internal explosion; suchhousings are well known in the art. Closure disk 9 and housing wall 10are so related as to withstand the maximum pressures encountered, andare provided with enough engaging threads to prevent the passage offlame and hot gases.

The exterior surface of housing wall 15 in the region 20 containingopening 16 is substantially planar. Unless the exterior of wall 15inherently is flat within extremely close tolerances, the wall region 20surrounding opening 16 is subjected to the action of a milling machineor the like. As shown in FIGS. 1 and 2, wall 15 may be subjected tomilling action in region 20 from the front to the rear of the housing,thereby creating :a groove of substantial width and length in theexterior surface of the wall.

In most instances it is desirable that this wall region be planar withintolerances of about plus or minus 0.0015 inch.

An imperforate seal plate 25 is secured to housing wall 15 in the region20 containing opening 16, the seal plate overlying the opening. The rearsurface 26 (FIG. 5) of seal plate 25, like region 29 of wall 15, issubstantially planar. This surface, as shown in FIG. 3, bears on region20 of the wall when seal plate 25 is secured in position. In most casessurface 26 also should be planar within tolerances of about plus orminus 0.0015 inch so that clearance between plate and wall will notexceed 0.0030 inch.

As shown, seal plate 25 is secured to Wall 15 by means of beaded bolts30 extending through snug openings 31 (FIGS. 35) in the plate andthreaded into openings 32 in wall 15. Four bolts 30 are shown, and theyare spaced more or less uniformly around opening 16 in the wall.

Abutting surfaces 20 and 26 of wall 15 and plate 25 have registeringsemi-circular grooves leading from one edge of plate 25 to opening 16.Thus, wall 15 has semicircular groove 35 which, as shown, extends fromopening 16 to the wall edge, and plate 25 has registering semicirculargroove 36.

Semi-circular grooves 35 and 36 best are formed in wall 15 and plate 25when the latter is secured in place on the wall. At that time, it is asimple matter to drill the two grooves at once, the axis of the drilldirected in the hearing plane, thus forming a passage having a circularcross section.

A lead-in element 40 (FIG. 1), such as a capillary tube, lies in theregistering grooves 35 and 36 and extends from the outside to the insideof housing 6 through wall opening 16. For necessary effectiveexplosion-proof sealing the diameter of capillary tube 40 is about equalto the diameter of the passage formed by grooves 35 and 36, and in anyevent the clearance should not exceed about 0.0030 inch.

In those instances where the lead-in element, such as capillary tube 40,cannot tolerate appreciable deformation, semi-circular groove 35 in wall15 extends somewhat beyond the edge of overlying seal plate 25. Such anextension of groove 35 is shown at 42 in FIGS. 2 and 3. Similarly,semi-circular groove 36 in the bearing surface of plate 25 extendssomewhat beyond the margin of opening 16 in the wall. Such an extensionof groove 36 is shown at 43 in FIG. 5.

Seal plate 25 usually is mounted more or less centrally over opening 16in wall 15. It has been found that the minimum distance plate 25 extendsbeyond the margin of the opening is about 0.500 inch to insure desiredresults.

lthough seal plate 25 may have various shapes, the illustrated sealplate of rectangular shape has been found particularly satisfactory.With a plate of such shape, semicircular groove 36 therein is generallyparallel to the longer plate edges.

From the above description it is thought that the construction andadvantages of this invention will be readily apparent to those skilledin the art. Various changes in detail may be made without departing fromthe spirit or losing the advantages of the invention.

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is:

1. Explosion-proof lead-in structure comprising:

a housing wall having an opening therein, said wall constituting oneWall of a sealed switch housing subject to infiltration by explosivegases and subsequent internal explosion, a surface of said wall in theregion containing said opening substantially planar;

an imperforate seal plate secured to said surface of said wall in theregion containing said opening and overlying said opening, the surfaceof said plate bearing on said wall substantially planar;

the abutting surfaces of said wall and said plate in view of the lengthsthereof being planar within tolerances which provide a seal between saidsurfaces preventing passage of flame and hot gases from the inside tothe outside of the housing following an internal explosion therein;

the abutting surfaces of said wall and plate having registeringsemi-circular grooves therein leading from one edge of said plate tosaid opening; and

a tubular lead-in element of circular cross section having a portionextending through said registering grooves and an end portion extendingthru said opening from one side of said wall to the other, the diameterof the passage formed by said grooves about equal to the diameter ofsaid lead-in element, the maximum clearance between the walls of saidpassage and said tubular lead-in element in view of the lengths thereofbeing less than an amount permitting passage of flame and hot gases fromthe inside to the outside of the housing following an internalexplosiOn.

2. The combination of claim 1 wherein said lead-in element is acapillary tube.

3. The combination of claim 1 wherein the groove in said wall extendsbeyond the adjacent edge of said seal plate and the groove in said plateextends beyond the margin of the opening.

4. The combination of claim 1 wherein said seal plate is rectangular,and the groove therein is generally parallel to the longer plate edges.

5. The combination of claim 1 wherein said seal plate is locatedgenerally centrally over the opening in said wall.

6. The combination of claim 1 wherein the bearing surfaces of said Walland said plate are planar within tolerances of about plus or minus0.0015 inch.

7. The combination of claim 6 wherein the minimum distance said plateextends beyond the margin of the opening in said wall is about 0.500inch.

References Cited UNITED STATES PATENTS 1,741,823 12/1929 Burg 2s51941,786,146 12/1930 Bucklein 2s5 1s9 x 2,939,022 5/1960 Groutage 17467 xCARL W. TCMLIN, Primary Examiner.

EDWARD C. ALLEN, Examiner.

A. V. KUNDRAT, Assistant Examiner.

1. EXPLOSION-PROOF LEAD-IN STRUCTURE COMPRISING: A HOUSING WALL HAVINGAN OPENING THEREIN, SAID WALL CONSTITUTING ONE WALL OF A SEALED SWITCHHOUSING SUBJECT TO INFILTRATION BY EXPLOSIVE GASES AND SUBSEQUENTINTERNAL EXPLOSION, A SURFACE OF SAID WALL IN THE REGION CONTAINING SAIDOPENING SUBSTANTIALLY PLANAR; AN IMPERFORATE SEAL PLATE SECURED TO SAIDSURFACE OF SAID WALL IN THE REGION CONTAINING SAID OPENING AND OVERLYINGSAID OPENING, THE SURFACE OF SAID PLATE BEARING ON SAID WALLSUBSTANTIALLY PLANAR; THE ABUTTING SURFACES OF SAID WALL AND SAID PLATEIN VIEW OF THE LENGTHS THEREOF BEING PLANAR WITHIN TOLERANCES WHICHPROVIDE A SEAL BETWEEN SAID SURFACES PREVENTING PASSAGE OF FLAME AND HOTGASES FROM THE INSIDE TO THE OUTSIDE OF THE HOUSING FOLLOWING ANINTERNAL EXPLOSION THEREIN; THE ABUTTING SURFACES OF SAID WALL AND PLATEHAVING REGISTERING SEMI-CIRCULAR GROOVES THEREIN LEADING FROM ONE EDGEOF SAID PLATE TO SAID OPENING; AND A TUBULAR LEAD-IN ELEMENT OF CIRCULARCROSS SECTION HAVING A PORTION EXTENDING THROUGH SAID REGISTERINGGROOVES AND AN END PORTION EXTENDING THRU SAID OPENING FROM ONE SIDE OFSAID WALL TO THE OTHER, THE DIAMETER OF THE PASSAGE FORMED BY SAIDGROOVES ABOUT EQUAL TO THE DIAMETER OF SAID LEAD-IN ELEMENT, THE MAXIMUMCLEARANCE BETWEEN THE WALLS OF SAID PASSAGE AND SAID TUBULAR LEAD-INELEMENT IN VIEW OF THE LENGTHS THEREOF BEING LESS THAN AN AMOUNTPERMITTING PASSAGE OF FLAME AND HOT GASES FROM THE INSIDE TO THE OUTSIDEOF THE HOUSING FOLLOWING AN INTERNAL EXPLOSION.